YAPF是Google开源的Python代码文件格式化工具

YAPF

Most of the current formatters for Python --- e.g., autopep8, and pep8ify --- are made to remove lint errors from code. This has some obvious limitations. For instance, code that conforms to the PEP 8 guidelines may not be reformatted. But it doesn't mean that the code looks good.

YAPF takes a different approach. It's based off of 'clang-format', developed by Daniel Jasper. In essence, the algorithm takes the code and reformats it to the best formatting that conforms to the style guide, even if the original code didn't violate the style guide. The idea is also similar to the 'gofmt' tool for the Go programming language: end all holy wars about formatting - if the whole codebase of a project is simply piped through YAPF whenever modifications are made, the style remains consistent throughout the project and there's no point arguing about style in every code review.

The ultimate goal is that the code YAPF produces is as good as the code that a programmer would write if they were following the style guide. It takes away some of the drudgery of maintaining your code.

(optional) If you are using Python 2.7 and want to enable multiprocessing:

$ pip install futures

YAPF is still considered in "alpha" stage, and the released version may change often; therefore, the best way to keep up-to-date with the latest development is to clone this repository.

Note that if you intend to use YAPF as a command-line tool rather than as a library, installation is not necessary. YAPF supports being run as a directory by the Python interpreter. If you cloned/unzipped YAPF into DIR, it's possible to run:

YAPF supports Python 2.7 and 3.6.4+. (Note that some Python 3 features may fail to parse with Python versions before 3.6.4.)

YAPF requires the code it formats to be valid Python for the version YAPF itself runs under. Therefore, if you format Python 3 code with YAPF, run YAPF itself under Python 3 (and similarly for Python 2).

usage: yapf [-h] [-v] [-d | -i] [-r | -l START-END] [-e PATTERN]
[--style STYLE] [--style-help] [--no-local-style] [-p]
[-vv]
[files [files ...]]
Formatter for Python code.
positional arguments:
files
optional arguments:
-h, --help show this help message and exit
-v, --version show version number and exit
-d, --diff print the diff for the fixed source
-i, --in-place make changes to files in place
-r, --recursive run recursively over directories
-l START-END, --lines START-END
range of lines to reformat, one-based
-e PATTERN, --exclude PATTERN
patterns for files to exclude from formatting
--style STYLE specify formatting style: either a style name (for
example "pep8" or "google"), or the name of a file
with style settings. The default is pep8 unless a
.style.yapf or setup.cfg file located in the same
directory as the source or one of its parent
directories (for stdin, the current directory is
used).
--style-help show style settings and exit; this output can be saved
to .style.yapf to make your settings permanent
--no-local-style don't search for local style definition
-p, --parallel Run yapf in parallel when formatting multiple files.
Requires concurrent.futures in Python 2.X
-vv, --verbose Print out file names while processing

The formatting style used by YAPF is configurable and there are many "knobs" that can be used to tune how YAPF does formatting. See the style.py module for the full list.

To control the style, run YAPF with the --style argument. It accepts one of the predefined styles (e.g., pep8 or google), a path to a configuration file that specifies the desired style, or a dictionary of key/value pairs.

The config file is a simple listing of (case-insensitive) key = value pairs with a [yapf] heading. For example:

A lines argument: A list of tuples of lines (ints), [start, end], that we want to format. The lines are 1-based indexed. It can be used by third-party code (e.g., IDEs) when reformatting a snippet of code rather than a whole file.

For options FIXED, and VALIGN-RIGHT are only available when USE_TABS is enabled.

CONTINUATION_INDENT_WIDTH

Indent width used for line continuations.

DEDENT_CLOSING_BRACKETS

Put closing brackets on a separate line, dedented, if the bracketed expression can't fit in a single line. Applies to all kinds of brackets, including function definitions and calls. For example:

config = {
'key1': 'value1',
'key2': 'value2',
} # <--- this bracket is dedented and on a separate line
time_series =self.remote_client.query_entity_counters(
entity='dev3246.region1',
key='dns.query_latency_tcp',
transform=Transformation.AVERAGE(window=timedelta(seconds=60)),
start_ts=now()-timedelta(days=3),
end_ts=now(),
) # <--- this bracket is dedented and on a separate line

DISABLE_ENDING_COMMA_HEURISTIC

Disable the heuristic which places each list element on a separate line if the list is comma-terminated.

EACH_DICT_ENTRY_ON_SEPARATE_LINE

Place each dictionary entry onto its own line.

I18N_COMMENT

The regex for an internationalization comment. The presence of this comment stops reformatting of that line, because the comments are required to be next to the string they translate.

I18N_FUNCTION_CALL

The internationalization function call names. The presence of this function stops reformatting on that line, because the string it has cannot be moved away from the i18n comment.

INDENT_DICTIONARY_VALUE

Indent the dictionary value if it cannot fit on the same line as the dictionary key. For example:

config = {
'key1':
'value1',
'key2': value1 +
value2,
}

INDENT_WIDTH

The number of columns to use for indentation.

INDENT_BLANK_LINES

Set to
True to prefer indented blank lines rather than empty

JOIN_MULTIPLE_LINES

Join short lines into one line. E.g., single line
if statements.

NO_SPACES_AROUND_SELECTED_BINARY_OPERATORS

Do not include spaces around selected binary operators. For example:

1+2*3-4/5

will be formatted as follows when configured with *,/:

1+2*3-4/5

SPACES_AROUND_POWER_OPERATOR

Set to
True to prefer using spaces around
**.

SPACES_AROUND_DEFAULT_OR_NAMED_ASSIGN

Set to
True to prefer spaces around the assignment operator for default or keyword arguments.

SPACES_BEFORE_COMMENT

The number of spaces required before a trailing comment. This can be a single value (representing the number of spaces before each trailing comment) or list of of values (representing alignment column values; trailing comments within a block will be aligned to the first column value that is greater than the maximum line length within the block). For example:

With spaces_before_comment=5:

1 + 1 # Adding values

will be formatted as:

1 + 1 # Adding values <-- 5 spaces between the end of the statement and comment

With spaces_before_comment=15, 20:

1 + 1 # Adding values two + two # More adding

longer_statement # This is a longer statement short # This is a shorter statement

a_very_long_statement_that_extends_beyond_the_final_column # Comment short # This is a shorter statement

will be formatted as:

1 + 1 # Adding values <-- end of line comments in block aligned to col 15 two + two # More adding

longer_statement # This is a longer statement <-- end of line comments in block aligned to col 20 short # This is a shorter statement

a_very_long_statement_that_extends_beyond_the_final_column # Comment <-- the end of line comments are aligned based on the line length short # This is a shorter statement

SPACE_BETWEEN_ENDING_COMMA_AND_CLOSING_BRACKET

Insert a space between the ending comma and closing bracket of a list, etc.

SPLIT_ARGUMENTS_WHEN_COMMA_TERMINATED

Split before arguments if the argument list is terminated by a comma.

SPLIT_ALL_COMMA_SEPARATED_VALUES

If a comma separated list (dict, list, tuple, or function def) is on a line that is too long, split such that all elements are on a single line.

SPLIT_BEFORE_BITWISE_OPERATOR

Set to
True to prefer splitting before
&,
| or
^ rather than after.

SPLIT_BEFORE_CLOSING_BRACKET

Split before the closing bracket if a list or dict literal doesn't fit on a single line.

SPLIT_BEFORE_DICT_SET_GENERATOR

Split before a dictionary or set generator (comp_for). For example, note the split before the for:

Split after the opening paren which surrounds an expression if it doesn't fit on a single line.

SPLIT_BEFORE_FIRST_ARGUMENT

If an argument / parameter list is going to be split, then split before the first argument.

SPLIT_BEFORE_LOGICAL_OPERATOR

Set to
True to prefer splitting before
and or
or rather than after.

SPLIT_BEFORE_NAMED_ASSIGNS

Split named assignments onto individual lines.

SPLIT_COMPLEX_COMPREHENSION

For list comprehensions and generator expressions with multiple clauses (e.g multiple "for" calls, "if" filter expressions) and which need to be reflowed, split each clause onto its own line. For example:

To preserve the nice dedented closing brackets, use the dedent_closing_brackets in your style. Note that in this case all brackets, including function definitions and calls, are going to use that style. This provides consistency across the formatted codebase.

We wanted to use clang-format's reformatting algorithm. It's very powerful and designed to come up with the best formatting possible. Existing tools were created with different goals in mind, and would require extensive modifications to convert to using clang-format's algorithm.

The main data structure in YAPF is the UnwrappedLine object. It holds a list of FormatTokens, that we would want to place on a single line if there were no column limit. An exception being a comment in the middle of an expression statement will force the line to be formatted on more than one line. The formatter works on one UnwrappedLine object at a time.

An UnwrappedLine typically won't affect the formatting of lines before or after it. There is a part of the algorithm that may join two or more UnwrappedLines into one line. For instance, an if-then statement with a short body can be placed on a single line:

if a ==42: continue

YAPF's formatting algorithm creates a weighted tree that acts as the solution space for the algorithm. Each node in the tree represents the result of a formatting decision --- i.e., whether to split or not to split before a token. Each formatting decision has a cost associated with it. Therefore, the cost is realized on the edge between two nodes. (In reality, the weighted tree doesn't have separate edge objects, so the cost resides on the nodes themselves.)

For example, take the following Python code snippet. For the sake of this example, assume that line (1) violates the column limit restriction and needs to be reformatted.

For line (1), the algorithm will build a tree where each node (a FormattingDecisionState object) is the state of the line at that token given the decision to split before the token or not. Note: the FormatDecisionState objects are copied by value so each node in the graph is unique and a change in one doesn't affect other nodes.

Heuristics are used to determine the costs of splitting or not splitting. Because a node holds the state of the tree up to a token's insertion, it can easily determine if a splitting decision will violate one of the style requirements. For instance, the heuristic is able to apply an extra penalty to the edge when not splitting between the previous token and the one being added.

There are some instances where we will never want to split the line, because doing so will always be detrimental (i.e., it will require a backslash-newline, which is very rarely desirable). For line (1), we will never want to split the first three tokens: def, xxxxxxxxxxx, and (. Nor will we want to split between the ) and the : at the end. These regions are said to be "unbreakable." This is reflected in the tree by there not being a "split" decision (left hand branch) within the unbreakable region.

Now that we have the tree, we determine what the "best" formatting is by finding the path through the tree with the lowest cost.

And that's it!

YAPF is not an official Google product (experimental or otherwise), it is just code that happens to be owned by Google.